#include <iostream>
using namespace std;
void test1(){
    string str="hello world";
    str=str+"hello cpp";
    cout<<str<<endl;
    str+='A';
    cout<<str<<endl;
    str.append("hello linux");
    cout<<str<<endl;
}
    
int main(int argc, char * argv[]){
    test1();
    return 0;
}

